The present invention relates to a method and to apparatus for oxygen cutting continuously cast billets.
In general, steel working installations for continuously casting billets include oxygen cutting apparatus serving to cut up the billet leaving the casting apparatus into segments for rolling into steel products (round bars, sections, wires, etc . . . ). Conventionally, oxygen cutting apparatuses make use of a carriage that is horizontally displaceable on associated rails passing over the billet to be cut. The carriage has a bottom clamp for taking hold of the moving billet and, ahead of the carriage, a torch carrier together with its torch that is suitable for being made to swing in a vertical plane by associated drive means. The moving carriage is motor-driven, and motor drive is declutched when the clamp is actuated since the carriage is then driven directly by the moving billet. The swinging torch is then put into action and performs oxygen cutting, the cutting oxygen jet passing vertically through the billet from its top face. Thus, while the carriage is moving in translation identically to the billet during the time required for cutting, the billet is cut by the swinging movement of the oxygen cutting torch in a vertical plane. Once the billet has been cut, the carriage is caused to move back and the clamp is actuated again to take hold of the billet further upstream so as to make a new cut. Document EP-A-0 639 416 describes an oxygen cutting installation having two lines, each with its own moving carriage having a respective swinging torch of the type described above.
That type of oxygen cutting technique when applied to continuously cast billets presents three major drawbacks.
The first drawback lies in the formation of molten metal residue on the bottom face of the billet where the oxygen jet leaves it, with this occurring over the entire width of the billet. This rim of molten metal residue mixed with iron oxide remains securely attached to the cut ends and forms a cutting bead which is naturally undesirable. It turns out to be necessary to make provision for an additional operation of removing such residue or beads of greater or lesser size depending on the grade of steel and on the type and adjustment of the torch. This removal is generally performed by trimming, in general by means of a torch. This is a correction operation leading to a cost penalty in billet production.
The second drawback lies in the oxygen cutting jet being used in an unfavorable manner which is a direct consequence of the geometrical motion of the torch whereby it follows a circular arc in a vertical plane while the torch carrier is swinging. The jet travels at a speed that is greater at the bottom face of the billet than it is on the top or xe2x80x9cattackxe2x80x9d face of said billet, which is unfavorable in energy terms insofar as the cutting oxygen is less energetic at the downstream edge of the cut because it has lost kinetic energy. Unfortunately, the thickness of the cutting bead is a function of the speed of the oxygen cutting jet, such that the bead is automatically very thick if it is desired to cut the billet quickly.
Finally, a third drawback can be mentioned which is failure to accommodate any accidental twisting of the billet (on cooling with certain steels), which twisting gives rise to cutting being inaccurate, and the presence of residue that is necessarily greater in the most twisted zones of the billet.
The technological background is also illustrated by document US-A-2 820 420 which describes an oxygen cutting torch cantilevered out from a horizontally-movable carriage, and by document WO-A-96/20818 which describes a traveling crane supporting a telescopically-extensible vertical working arm.
The invention seeks to provide an oxygen cutting technique that makes it possible to avoid the above-specified drawbacks.
An object of the invention is thus to provide a method of oxygen cutting continuously cast billets, and apparatus for implementing the method, capable of cutting billets in regular manner without leaving a cutting bead, and to do so with high accuracy and great speed, even in the event of billets being accidentally twisted.
According to the invention, this problem is resolved by a method of Oxygen cutting continuously cast billets, wherein a cutting member and a trimming member are positioned relative to the billet to be cut by taking a reference directly on the billet, and then the cutting member and the trimming member are lowered parallel to the side faces of the billet so as to perform cutting progressively downwards by attacking one of the side faces of the billet horizontally or substantially horizontally, and while simultaneously trimming the cutting bead that forms on the other side face by attacking said other side face constantly in a downward direction.
Thus, by taking a reference directly on the billet, it is guaranteed that an accurate cut will be made which starts on a side face of the billet in a direction that is exactly perpendicular thereto, even if the billet is twisted. When the billet is twisted, the direction of attack is automatically corrected. This makes it possible to achieve genuine xe2x80x9chorizontalxe2x80x9d cutting with optimum accuracy and speed.
Preferably, the reference is taken directly on the two side faces of the billet, preferably by means of a moving clamp. When the moving clamp has contacted the two side faces of the billet, the direction in which the cutting member and the trimming member move downwards is accurately determined, and it is quite certain that this direction is indeed parallel to the side faces of the billet.
Also advantageously, the reference is taken by lowering a moving clamp quickly, after which cutting and trimming are performed downwards by lowering the corresponding members at a programmed oxygen cutting speed. This optimizes the oxygen cutting process with minimum loss of time for putting the cutting and trimming members into place.
Also preferably, the trimming member is a blow torch nozzle whose jet remains continuously directed downwards while the cutting and trimming members are being lowered.
Thus, the simultaneous trimming performed by action that is constantly directly downwards, in particular by a jet from a nozzle, causes fumes to be removed downwards, which favors normal removal of the fumes, and in addition it avoids causing slag to be splashed sideways as happens conventionally with installations in which the torch is moved with a swinging motion. Thus, for the first time, a horizontal cut can be provided that has no cutting bead and in which trimming is organized downwards.
The invention also provides apparatus for implementing the above oxygen cutting method, the apparatus being of the type comprising a carriage that is horizontally displaceable on associated rails overlying the billet to be cut.
According to the invention, the apparatus further comprises:
an auxiliary structure connected to the moving carriage and supporting a vertical actuator; and
a frame suspended from the vertical actuator via a universal joint, said frame supporting both a moving clamp and a cutting member and trimming member that are movable in a vertical or substantially vertical direction as determined by the moving clamp after it has been clamped the billet to be cut, said cutting member acting in a substantially horizontal direction essentially perpendicular to the above-specified displacement direction, and said trimming member acting downwards.
Because of the universal joint, it is possible to move the cutting and trimming members in a direction that slopes relative to the vertical, which direction is automatically given by the reference being taken by means of the moving clamp.
Preferably, the vertical actuator is a piston-and-cylinder or an electric motor, with the body thereof being floatingly mounted on the auxiliary structure, being capable at least of pivoting about a horizontal axis parallel to the travel direction of the carriage. This avoids any risk of jamming for the assembly which is moved in a vertical plane for cutting the billet horizontally.
In a particular embodiment, the auxiliary structure is mounted via one end to the front of the carriage so as to be pivotable about a horizontal axis, and rests via its other end on the same rails as the carriage.
In a variant, provision can be made for the auxiliary structure to be mounted laterally on the running axles of the carriage, and to be extended forwards by a cantilevered-out portion which supports the vertical actuator.
The cutting member and the trimming member can be connected to the frame in various different ways providing the sliding direction of the cutting and trimming members complies with the direction given by the reference taken by means of the moving clamp.
Thus, it is possible to provide for the cutting member and the trimming member to be connected to a central slide passing through the frame, and for the moving clamp to be hinged on said frame.
In a variant, provision can be made for the cutting member and the trimming member to be connected to the frame, and the moving clamp to be hinged to a secondary structure capable of sliding vertically on said frame. In which case, the secondary structure can be connected to the frame by an actuator for lowering the clamp.
Preferably, the cutting member comprises a horizontal burner having an incorporated nozzle block. It is then advantageous for the nozzle block with its cutting oxygen feed pipe to form a removable assembly.
Also advantageously, the trimming member is a nozzle fed with oxygen, and mounted in such a manner that its jet is directed downwards. In which case it is preferable for the trimming nozzle to be fed with the cutting oxygen or the heating oxygen as fed to the cutting member via an associated branch connection.